1. Field of the Invention
The present invention is directed to X-ray inspection technology, and more particularly, to a system and method for high-energy X-ray inspection of loaded vehicles (container or general cargo), and more particularly, to effective screening cargo at critical facilities, seaports and border crossing.
2. Description of the Related Art
Many systems for radiation inspection of trucks and containers are known, most of which are, generally, based on the same principle, general of X-ray radiation by and X-ray source, forming, using a collimator, a fan-shaped X-ray beam directed at the vehicle, scanning the vehicle using the fan-shaped beam, and converting the detected radiation, after it passes through the vehicle, into a digital signal, which is then processed into an image for viewing by an operator. Such systems generally are designed with several goals in mind.
Some X-ray inspection systems are geared towards a high degree of mobility, primarily through the use of modular construction; see, for example, RU 2251683. Other systems solve the mobility problem by placing the X-ray source on one vehicle, while the detector is located on a different vehicle. The two vehicles are then electronically tied together, so that they move in sync with each other, see U.S. Pat. No. 6,937,692. Another alternative is placing the X-ray source on a vehicle, while the detector is located on a moving or rotatable portal. The portal moves along the vehicle or container that is being inspected, together with the vehicle on which the detector is located, see, for example, U.S. Pat. Nos. 5,692,028, 5,903,623, 7,517,149, 7,497,618, and FR 2808088.
Systems that have moving sources and detectors of X-ray radiation typically have fairly low throughput (measured in terms of number of vehicles per unit time), which is generally due to a relatively low scanning speed (typically in the range of 0.2-0.8 meters per second), as well as due to the need for the driver to leave the inspection area, or to at least stand sufficiently far from the radiation source (which results in substantial loss of time to both the operators of the inspection system and to the drivers); also, a relatively large area around the scanner needs to be reserved, due to the possible radiation exposure. Since the radiation source is mobile, and moves, therefore, the exclusion zone from where humans should not be present during scans correspondingly increases. Also, such systems suffer from reliability problems due to the presence of moving parts, and require significant maintenance efforts. Additionally, when both the source and the detector are in motion during the scan, the vibration effects cause fuzziness in the image, and lack of clarity. Therefore, one of the objectives of the present invention is to improve the quality of the data collected by the inspection station, while reducing its size, footprint, and maintenance requirements.
Stationary X-ray inspection systems are also known, where the vehicle is moved through the stationery portal on a special conveyor type mechanism (see, for example, U.S. Pat. Nos. 5,091,924 and 6,542,580). In this case, the problem of image quality is at least partly addressed, and the exclusion zone around the inspection station can be reduced. However, the throughput of such scanning system tends to be fairly low, due to low scanning speed, and the need for the driver of the vehicle to leave the inspection area due to high radiation dosage use.
The throughput of the scanner can be significantly increased in systems with stationery sources and detectors, if the vehicles move through the scanners on their own power, and under control of their drivers. The problem of radiation exposure for the driver is solved by only turning the X-ray source on after the driver has moved past the source (which can be detected, for example, by using a special tag or a bar code on the vehicle, see, for example, U.S. Pat. No. 7,308,076). However, full radiation safety is still not achieved in this case, for example, for people who might be in the cargo hold of a truck, such as illegal immigrants, or for the driver's themselves, who are still exposed to at least some scattered radiation. Thus, one of the objectives of the present invention is reducing the dosage of radiation used to scan the vehicle, while maintaining the quality of the image.
Also known are systems for detection of radioactive materials in an automobile, such as, for example, described in U.S. Pat. No. 7,239,245, which use an autonomous device with its own service personnel and control equipment. A heretofore unresolved problem however is forming an integrated system of monitoring a control that permits monitoring and detection of radioactive materials in automobiles and X-ray scanning and control from a single operations center.
U.S. Patent Publication No. 2009/086907 describes a method for X-ray control of automobiles that includes generation of X-ray radiation as to different energies by an X-ray source, forming, using a collimator of a fan-shaped X-ray beam that is directed at a automobile moving under its own power, detecting the X-ray beam after it passes through the automobile, and converting the detected X-ray beam into a digital electronic signal that can then be used to form an image of the automobile, taking into account the speed of the automobile.
U.S. Patent Publication No. 2009/086907 also describes a portal for X-ray scanning of an automobile, where the portal carries the collimator for forming the fan-shaped beam and also carries the detector of the X-rays. The portal also carries the electronics required for converting the detected radiation into a digital signal. In this case, the X-ray source and the collimator are located on a top bulkhead of the portal, which adds instability to the entire construction, while the X-ray detector is buried under the road. Also, the described system uses a relatively low energy radiation source (140 KeV), which is only useful for X-ray monitoring of cars, which typically have metal body thickness of about 3 mm. On the other hand, large automobiles, trucks, containers or container carriers typically cannot be scanned using the system, since they frequently have too much metal (often as much as 300 mm thick between the X-ray source and the detector), as well as due to the pressure exerted by the heavy vehicles on the road, which can affect the radiation detector buried under the road.